Vehicle wheel rolling bearings with a sealing device integrated with a magnetic encoder to detect wheel rotation speed are known.
For example as shown in FIG. 4, a vehicle wheel rolling bearing has first and second annular sealing plates 62 and 63 fitted, respectively, on an inner ring 60 and an outer ring 61. Each of these sealing plates 62 and 63 has a substantially “L”-shaped cross-section formed, respectively, by a cylindrical portion 62a and 63a and a radially extending portion 62b and 63b. The sealing plates 62 and 63 are arranged opposite to each other. The radially extending portion 62b of the first sealing plate 62 has an encoder 64 to detect the wheel rotation speed. The encoder is bonded to the portion 62b, via vulcanization, at the inboard side of the bearing. The encoder 64 is made of a rubber magnet where magnetic substance powder is mingled and N and S poles are alternately magnetized along the circumferential direction of the encoder.
The second sealing plate 63 has a sealing member 65 bonded via vulcanization. The sealing member 65 has an integrally formed side lip 65a that slidably contacts with the radially extending portion 62b of the first sealing plate 62b. Other integrally formed radial lips 65b and 65c slidably contact with the cylindrical portion 62a. A tip of the radially extending portion 62b of the first sealing plate 62 opposes the cylindrical portion 63a of the second sealing plate 63. A slight radial gap is formed between the two forming a labyrinth seal 66.
In such a vehicle wheel rolling bearing with the sealing device integrated with the magnetic encoder, dust or sand sometimes enter into a gap formed between the surfaces of the encoder 64 and a detecting sensor (not shown) arranged opposite to the encoder 64. Thus, the dust or sand may abrade or damage the surface of the encoder 64. This is because the encoder 64 is mounted on the inboard side of the first sealing plate 62 forming a slinger and is exposed to ambient circumstances. In order to overcome this problem, a vehicle wheel rolling bearing has been proposed as shown in FIG. 5.
In this rolling bearing, a pulse generating ring 71, comprising a holding plate 71a and an encoder 71b magnetized in multipoles, is fitted on a rotating inner ring 70. The encoder 71b is made, for example, of elastomer filled with magnetic pieces and bonded to the holding plate 71a, via vulcanization. A cover member 72, made of non-ferromagnetic material, is mounted on an outer ring 73 of the stationary side. The cover 72 has a sealing lip 74 bonded via vulcanization. This sealing lip 74 slidably contacts the pulse generating ring 71 and protects the encoder 71b from influences from ambient circumstances. A detecting sensor 75 directly contacts the cover member 72. Radio signals are transmitted through the cover member 72. Thus, it is possible to prevent the penetration of dust or sand into a gap formed between the surfaces of the encoder 71b and detecting sensor 75. Accordingly, abrasion or damage to the surface of the encoder 71b is prevented.
Japanese Laid-open Patent Publication No. 160744/1998 illustrates such a vehicle wheel rolling bearing. However, since the pulse generating ring 71 is arranged so that it radially extends and the signal detection of the detecting sensor 75 is carried out through the cover member 72, it is difficult to ensure sufficient area of the pulse generating ring 71 because of the limitation of radial space of the bearing and thus detecting sensitivity is also reduced. In addition, although the cover member 72 can prevent penetration of dust or sand into the space of the encoder 71b, it increases the distance between the encoder 71b and the detecting sensor 75 further reducing detecting sensitivity.